Association of Maternal Comorbidity Burden With Cesarean Birth Rate Among Nulliparous, Term, Singleton, Vertex Pregnancies

This cross-sectional study aims to determine the association between obstetric comorbidity index score and cesarean delivery among nulliparous, term, singleton, vertex pregnancies and to evaluate whether disparities in mode of delivery exist based on race and ethnicity group after adjusting for covariate factors.


Introduction
Although cesarean delivery is a valuable and potentially lifesaving intervention in many cases, the rapid increase in use of the procedure in the early 2000s was without clear medical justification. 1 Hospitals with higher cesarean delivery rates have higher rates of severe maternal morbidity (SMM). 2 Maternal mortality occurs more frequently after cesarean birth than after vaginal birth. 3,4After cesarean birth, there is an increased risk of developing complications in future pregnancies, including placental abnormalities such as placenta previa and placenta accreta. 4Patients with nulliparous, term, singleton, vertex (NTSV) pregnancies are a critical target population for reducing the overall cesarean delivery rate. 5,6Reduction of cesarean birth in this group is considered a national priority, and it has become a standard quality measure in obstetrical care.Nulliparous, term, singleton, vertex pregnancies are thought to have the most favorable conditions for vaginal birth, and these patients have been described as "low risk," a largely true but somewhat oversimplified characterization.8][9] Specifically, the prevalence of hypertension, diabetes, thyroid disorders, autoimmune disorders, asthma, and mental health conditions have substantially increased. 10,11Furthermore, certain neurological and cardiac conditions that were once considered rare or incompatible with pregnancy are now seen with increasing frequency in pregnant patients. 12 is well established that maternal comorbidity burden is associated with risk of SMM, 13 but there are relatively limited data on how the number and type of preexisting conditions affect mode of delivery among first-time pregnant patients. 14,15The obstetric comorbidity index (OB-CMI) screening tool was originally developed and validated by Bateman et al 16 to predict SMM using utilization claims data.This weighted scoring system was later revised by Easter et al 17 to incorporate additional clinical data not reliably obtained in health care utilization data sets.The OB-CMI score has also been used to study other clinical outcomes, such as use of general anesthesia for cesarean delivery. 180][21][22][23] Moreover, it remains unclear how the number of maternal comorbidities differ across race and ethnicity groups and whether this affects the rate of cesarean birth.
The primary objective of this study was to determine the association between maternal comorbidity burden, as quantified by OB-CMI score (calculated at time of admission), and cesarean delivery among NTSV pregnancies.There were 2 secondary objectives: (1) to evaluate whether disparities in mode of delivery exist based on race and ethnicity group after adjusting for covariate factors, and (2) to evaluate whether indication for cesarean delivery differed by OB-CMI and race and ethnicity groups.We hypothesized that there would be a positive association between OB-CMI score and cesarean delivery rate and that differences across race and ethnicity groups, if present, could be partially explained by differences in OB-CMI score.

Patient Population
This was a retrospective cross-sectional study of all patients with NTSV pregnancies who delivered between January 2019 and December 2021 at 7 hospitals within a large academic health system in New York.These facilities serve a diverse patient population that resides in both urban and suburban communities and represents the full socioeconomic spectrum.Inclusion criteria were NTSV pregnancies.Patients who did not meet the following NTSV criteria were excluded: multiparous patients, preterm deliveries (<37 weeks of gestational age), multiple gestations, and nonvertex presentations.Additional exclusion criteria were intrauterine fetal demise and contraindications to labor identified early in pregnancy, including placenta previa, vasa previa, prior myomectomy with disruption of endometrium, and suspected placenta accreta spectrum.
Clinical and demographic data were obtained from the inpatient electronic medical record system (Sunrise Clinical Manager [Allscripts]).Maternal comorbidities were identified by International Statistical Classification of Diseases, Tenth Revision, Clinical Modification codes and clinical documentation.Baseline demographic data included public health insurance (yes/no), preferred language English (yes/no), and self-identified race and ethnicity (American Indian or Alaska Native, Asian or Pacific Islander, Hispanic, non-Hispanic Black, non-Hispanic White, other or multiracial, and declined or unknown), which were selected from prespecified categories at the time of hospital admission.Clinical data included cesarean delivery (yes/no), indication for cesarean delivery, hospital, and limited perinatal outcomes.
The Northwell Health Institutional Review Board approved this study as minimal-risk research using data collected for routine clinical practice and thus waived the requirement for informed consent.The study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline.

Primary Outcome
The primary outcome was cesarean delivery, a binary variable.The OB-CMI score, the primary independent variable, was calculated at the time of admission for delivery hospitalization.This score is based on 24 weighted maternal comorbidity indicators as described by Easter et al. 17 At Northwell Health, a proprietary web application accessible to clinical directors and operations managers was implemented and automatically calculates this metric.This robust tool does not rely exclusively on diagnosis codes but also incorporates clinical documentation, thereby reducing misclassification of comorbidities and outcomes.During the study period, OB-CMI scores were not displayed directly on the electronic medical record interface; therefore, clinicians were blinded to the OB-CMI scores of patients under their care.The OB-CMI scores ranged from 0 to 18 among the included patients with NTSV pregnancies, and more than half of the patients had a score of 0. Therefore, for statistical analysis, this variable was recoded as a categorical factor where patients with an OB-CMI score of 0 were one category, and the remaining patients were subdivided into quartiles.Nonetheless, due to the skewed distribution of OB-CMI scores, perfect quartiles were not achieved, and the variable denoting OB-CMI score was recoded into the following OB-CMI groups: 0, 1, 2, 3, and 4 or higher.

Statistical Analysis
Descriptive statistics were used to characterize the demographic and clinical data.The χ 2 test was used to examine associations between categorical variables.For analysis of the primary outcome, multivariable mixed effects logistic regression, which incorporates fixed and random effects, was used to model the probability of a cesarean delivery as a function of the OB-CMI score group, where observations were nested within the hospital in which they occurred.Logistic regression was first performed with the OB-CMI group as the only independent variable in the model (ie, the unadjusted model).An adjusted logistic regression model was then created by adding potential covariates: race and ethnicity group, public health insurance, and preferred language.Adjusted odds ratios (AORs)

JAMA Network Open | Obstetrics and Gynecology
Maternal Comorbidity Burden and Cesarean Birth Among NTSV Pregnancies are presented along with the corresponding 95% CIs.Statistical significance was defined as 2-sided P < .05.The sample size for this study was based on availability of data from the inpatient database and not on any formal statistical power calculations.All analyses were conducted using SAS Enterprise Guide, release 3.8 (SAS Institute Inc).Because the study period was greatly affected by the COVID-19 pandemic, we evaluated whether there was an association between pandemic period (March 2020 onward) and cesarean birth.

Results
A total of 30 253 patients (mean [SD] age, 29.8 [5.4] years; 100% female) with NTSV pregnancies were included for analysis (Figure 1).The most common indication for cesarean birth was abnormal fetal status (4328 [50.2%]; eTable 3 in Supplement 1), which was seen more often for patients with an OB-CMI score of 0 compared with those with an OB-CMI score of 4 or higher (53.7% vs 43.0%, respectively; P < .001).
Non-Hispanic Black patients had statistically significant higher rates of abnormal fetal status than non-Hispanic White patients both overall (61.2% vs 44.4%, respectively) and across all OB-CMI score groups (eTable 4 in Supplement 1).
a Race and ethnicity were self-identified from prespecified categories at the time of hospital admission.

JAMA Network Open | Obstetrics and Gynecology
Maternal Comorbidity Burden and Cesarean Birth Among NTSV Pregnancies

Discussion Principal Findings
We observed that OB-CMI score was positively associated with cesarean delivery in a large, diverse population of patients with NTSV pregnancies.This may be characterized as a dose-response association between maternal comorbidity burden and cesarean delivery.Statistically significant differences in NTSV cesarean delivery rates were seen across race and ethnicity groups even after adjustment for preexisting maternal conditions.Specifically, among low-risk NTSV pregnancies without any maternal comorbidities (OB-CMI score of 0), non-Hispanic Black patients were at highest risk for cesarean birth.Interestingly, among higher OB-CMI groups (score of Ն3), cesarean birth rates did not differ when comparing race and ethnicity groups.Overall, non-Hispanic Black

JAMA Network Open | Obstetrics and Gynecology
Maternal Comorbidity Burden and Cesarean Birth Among NTSV Pregnancies

Results in the Context of What Is Known
Previous studies have evaluated the association of maternal comorbidities with NTSV cesarean birth rates, 14,20,24 and some have also examined scoring systems that summarize cumulative comorbidity burden. 15In contrast, the present approach builds on and enhances prior efforts by using a robust, validated comorbidity index that weighs diagnoses that reflect risk for SMM.In a national sample of NTSV pregnancies from 2016 to 2018, Andrikopoulou et al 14  White patients, those belonging to other race and ethnicity groups have a greater odds of cesarean delivery for nonreassuring fetal status. 21,27Based on the present findings, the frequency of cesarean birth for abnormal fetal status varies not only by race and ethnicity group, but also by OB-CMI score, overall occurring less often when OB-CMI score is 4 or higher.

Clinical Implications
The national NTSV cesarean delivery rate reported by the US Centers for Disease Control and Prevention increased to 26.3% in 2021. 28Healthy People 2030, the 10-year plan published by the US Department of Health and Human Services for addressing the country's most critical public health challenges, recommends a target rate of 23.6%. 29Unfortunately, there is no evidence-based optimal cesarean delivery rate shown to minimize adverse maternal and neonatal outcomes in all populations. 30Complex risk adjustments would be required to compare rates across institutions. 31rget rates established by health care quality organizations are often arbitrary and do not consider differences in patient characteristics.Based on the present findings, we expect that the cesarean delivery rate would be higher in a population with more comorbidities, regardless of whether those cesarean deliveries are necessarily indicated.The goal for such a population should be simultaneous efforts to reduce comorbidities and cesarean births.Establishing and incentivizing unattainable quality measures could have unexpected negative effects.
Several strategies have been proposed to safely lower the rate of primary cesarean delivery. 4terventions have been directed at patients (educational programs, childbirth workshops), health care professionals (peer review, mandatory second opinion, audit and feedback, review of evidencebased guidelines), and facilities (different staffing models), with varying success. 32There is evidence that standardized, evidence-based, induction and labor management protocols reduce the rate of cesarean delivery, particularly in racial and ethnic minority groups. 33Further efforts should be made to reduce modifiable risk factors and optimize chronic conditions before conception or early in gestation.In addition, nonclinical factors that may affect labor management must be explored, including social determinants of health, implicit bias, and structural as well as institutional racism.

Figure 3 .A
Figure 3. Cesarean Birth Rate by Race and Ethnicity and OB-CMI Score Among Nulliparous, Term, Singleton, Vertex Pregnancies

Table 1 .
Non-Hispanic White patients constituted the largest race and ethnicity group (43.7%), followed by Hispanic patients (16.2%),Asian or Pacific Islander patients (14.6%), and non-Hispanic Black patients (12.2%).Baseline characteristics of the study population are summarized in Table1(stratified results are summarized in eTables 1 and 2 in Supplement 1).Most patients had private health insurance (72.8%), spoke English as their preferred language (94.4%), had no comorbidities (56.7%), and were younger than 35 years of age at delivery (81.2%).The most Patients with public health insurance had a 19.4% lower odds of cesarean delivery (AOR, 0.81; 95% CI, 0.75-0.86)comparedwiththosewithout public health insurance.Preferred language of English was 6% higher odds of cesarean delivery (AOR, 1.18; 95% CI, 1.03-1.34).When the COVID-19 pandemic period (yes/no) was included as a covariate in the regression model (AOR, 1.06; 95% CI, 1.00-1.12),theotherresultswere nearly identical with each AOR, differing by 0.01.Given the very small effect size, pandemic period was not included in the final model.Figure3shows NTSV cesarean delivery rates for each race and ethnicity group stratified by OB-CMI score.A majority of non-Hispanic Black patients had 1 or more comorbidities (55.6%).For all other race and ethnicity groups, fewer than half of the patients had comorbidities.Compared with non-Hispanic White patients, non-Hispanic Black patients were 1.6 times more likely to have 1 or Baseline Demographics and Comorbidities (N = 30 253) common obstetric comorbidities were maternal age of 35 to 39 years (15.6%),preeclampsia/gestationalhypertension/chronichypertension(12.8%),asthma(6.7%),bodymassindex (BMI; calculated as weight in kilograms divided by height in meters squared) of 40 to 49.9 (6.0%), and preeclampsia with severe features or eclampsia (5.1%).The overall NTSV cesarean delivery rate was 28.5% (n = 8632); this rate varied from 18.4% to 32.5% across the 7 included hospitals (P < .001).Cesarean births increased after the onset of the COVID-19 pandemic, from 27.4% to 29.2% (P < .001).Figure2shows the prevalence of each OB-CMI score within the cohort and corresponding NTSV cesarean delivery rates.More than half of patients (56.7%) had no comorbidities that are components of the OB-CMI score.The cesarean birth rate increased from 22.1% among patients with an OB-CMI score of 0 to greater than 55% when OB-CMI scores were 7 or higher.On unadjusted analysis, there was a statistically significant association between OB-CMI score group and cesarean delivery.Results of multivariable mixed-effects logistic regression modeling are summarized in Table2.Each successive OB-CMI group had an increased risk, and patients with an OB-CMI score of 4 or higher had more than 3 times greater odds of a cesarean birth compared with patients with an OB-CMI score of 0 (AOR, 3.14; 95% CI, 2.90-3.40).The AORs for OB-CMI score groups did not change appreciably from the crude ORs in the unadjusted model.Compared with non-Hispanic White patients, all other race and ethnicity groups except for American Indian or Alaska Native (n = 188) were at increased risk for cesarean delivery after adjusting for other explanatory variables; non-Hispanic Black patients were at highest risk (AOR, 1.43; 95% CI, 1.31-1.55).JAMA Network Open | Obstetrics and GynecologyMaternal Comorbidity Burden and Cesarean Birth Among NTSV Pregnancies JAMA Network Open.2023;6(10):e2338604. doi:10.1001/jamanetworkopen.2023.38604(Reprinted) October 19, 2023 4/12 Downloaded From: https://jamanetwork.com/ on 10/21/2023 associated with 17.a Race and ethnicity were self-identified from prespecified categories at the time of hospital admission.b OB-CMI components excluded from study include multiple gestation, intrauterine fetal demise, placenta previa/suspected accreta, and previous cesarean delivery/myomectomy.JAMA Network Open | Obstetrics and Gynecology Maternal Comorbidity Burden and Cesarean Birth Among NTSV Pregnancies JAMA Network Open.2023;6(10):e2338604. doi:10.1001/jamanetworkopen.2023.38604(Reprinted) October 19, 2023 5/12 Downloaded From: https://jamanetwork.com/ on 10/21/2023

Table 2 .
Multivariable Mixed-Effects Logistic Regression Model for Cesarean Delivery Among NTSV Pregnancies After Adjusting for Covariate Factors

com/ on 10/21/2023 patients
had more comorbidities than patients from other race and ethnicity groups and were more likely to have cesarean deliveries performed for abnormal fetal status regardless of OB-CMI score.
20served an association between BMI, maternal age, and clinical factors such as diabetes and hypertension with cesarean birth.Other investigators have reported similar findings and acknowledged the additive effect of such characteristics.15Onechallenge in comparing such studies is that clinical groupings and definitions are inconsistent.Some authors classify overweight/obesity (BMI Ն25) as a comorbidity, whereas OB-CMI only incorporates class 3 obesity (BMI Ն40) and further differentiates the higher-risk subgroup with BMI greater than 50.Similarly, some authors classify any form of diabetes in pregnancy as a comorbidity, whereas OB-CMI only includes diabetes requiring insulin.More restrictive definitions may allow better identification of high-risk patients.The present finding that non-Hispanic White patients with NTSV pregnancies had a lower cesarean delivery rate compared with most other race and ethnicity groups is consistent with the findings reported by Okwandu and colleagues20in Northern California from 2016 to 2017, Edmonds and colleagues 25 in Massachusetts from 2006 to 2011, and Min and colleagues 26 in Maryland from 2004 to 2010.Despite different populations, geographies, clinical settings, and practice patterns, this finding persists.Furthermore, several investigators have reported that indications for cesarean delivery differ by racial and ethnic group, just as we report herein.Compared with non-Hispanic

Open | Obstetrics and Gynecology SUPPLEMENT 1. eTable 1.
Baseline demographics and comorbidities by obstetrical comorbidity index (OB-CMI) score group eTable 2. Baseline demographics and comorbidities by race and ethnicity group eTable 3. Cesarean delivery indications stratified by obstetrical comorbidity index (OB-CMI) score group and race and ethnicity group eTable 4. Cesarean delivery for abnormal fetal status stratified by obstetrical comorbidity index (OB-CMI) score group and race and ethnicity group eTable 5. Perinatal outcomes by obstetrical comorbidity index (OB-CMI) score group